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Subject[tip:perfcounters/urgent] x86: atomic64: The atomic64_t data type should be 8 bytes aligned on 32-bit too
Commit-ID:  bbf2a330d92c5afccfd17592ba9ccd50f41cf748
Gitweb: http://git.kernel.org/tip/bbf2a330d92c5afccfd17592ba9ccd50f41cf748
Author: Eric Dumazet <eric.dumazet@gmail.com>
AuthorDate: Fri, 3 Jul 2009 00:08:26 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Fri, 3 Jul 2009 13:26:38 +0200

x86: atomic64: The atomic64_t data type should be 8 bytes aligned on 32-bit too

Locked instructions on two cache lines at once are painful. If
atomic64_t uses two cache lines, my test program is 10x slower.

The chance for that is significant: 4/32 or 12.5%.

Make sure an atomic64_t is 8 bytes aligned.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
LKML-Reference: <alpine.LFD.2.01.0907021653030.3210@localhost.localdomain>
[ changed it to __aligned(8) as per Andrew's suggestion ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>


---
arch/x86/include/asm/atomic_32.h | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/arch/x86/include/asm/atomic_32.h b/arch/x86/include/asm/atomic_32.h
index 2503d4e..ae0fbb5 100644
--- a/arch/x86/include/asm/atomic_32.h
+++ b/arch/x86/include/asm/atomic_32.h
@@ -250,7 +250,7 @@ static inline int atomic_add_unless(atomic_t *v, int a, int u)
/* An 64bit atomic type */

typedef struct {
- unsigned long long counter;
+ unsigned long long __aligned(8) counter;
} atomic64_t;

#define ATOMIC64_INIT(val) { (val) }

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